Hedge trimmers are well known tools for cutting hedges and, more generally, vegetation from plants. Typically, a hedge trimmer includes a motor forming part of a drive train arranged to drive the motion of one or more suitably shaped blades, thereby to cut vegetation. Typically two toothed blades are provided and they are driven in relative reciprocating motion such that stems or leaves caught between a pair of teeth on one of the blades are cut as the teeth blade shear with a pair of teeth on the other of the blades. Since it is the movement of the blades relative to each other that is important, in some cases, one axially reciprocating blade is provided disposed adjacent a stationary blade, the teeth of the stationary blade providing a reaction force for the teeth of the reciprocating blade. In another example, both blades are caused to move so as to generate the required relative motion.
The motor for driving movement of the blade(s) may itself be powered by any appropriate power source. In one example, the motor is arranged to receive power from a battery such as a Li ion battery provided within the tool housing. In another example an AC mains connection is provided to the tool which supplies power to drive the motor. In the case of the power source being a battery, clearly the available power to the motor will be more limited given the physical limitations on battery power that derive from size and weight and the fact that the tool (containing the battery) needs to be light enough so that it can be used.
Whilst having a powerful motor is desirable, the more powerful a motor is, the larger it will tend to be. Accordingly, since the motor is for use in a hand-held tool, in terms of weight and the ease with which the tool can be manipulated, it is clearly desirable to have as small a motor as possible.
Known systems for powering hedge trimmers are disclosed in, for example, GB-A-1,406,244, GB-A-1,427,077, GB-A-848,325 and GB-A-884,387. In GB-A-884,387 a clutch is provided in a tool (an example of which is a hedge trimmer). The clutch also functions as a flywheel to provide the benefit of stored kinetic energy. The clutch, and therefore the flywheel, is arranged within the tool housing and is thus exposed to the air within the cavity defined by the housing. In use, it will generate and experience windage as a consequence. Windage may be considered the force of the air acting on the flywheel due to the relative movement between them or, conversely, the wind generated by the flywheel as it rotates.